Thin film resistor structure and method of fabricating a thin film resistor structure

ABSTRACT

A thin film resistor structure and a method of fabricating a thin film resistor structure is provided. The thin film resistor structure includes an electrical interface layer or head layer that is a combination of a Titanium (Ti) layer and a Titanium Nitride (TiN) layer. The combination of the Ti layer and the TiN layer mitigates resistance associated with the electrical interface layers.

This application is a division of Ser. No. 10/727,392, U.S. Pat. No.7,112,286, filed Dec. 4, 2003.

TECHNICAL FIELD

The present invention is directed to a thin film resistor structure anda method of fabricating a thin film resistor structure.

BACKGROUND OF THE INVENTION

Thin film resistors are very attractive components for high precisionanalog and mixed signal applications. In addition to a low thermalcoefficient of resistance and low voltage coefficient of resistance,thin film resistors provide good resistor matching and good stabilityunder thermal stress. To achieve good stability under thermal stress, itis critical to not only control the resistance of the body of the thinfilm resistor, but also the resistance of the electrical interface layerto the thin film resistor. Ideally, the resistance of the electricalinterface layer should not contribute to the resistance of the thin filmresistor.

Typically, thin film resistor fabrication processes implement titaniumtungsten (TiW) as an electrical interface layer to the thin filmresistor layer. A disadvantage associated with using titanium tungsten(TiW) as the electrical interface layer to the thin film resistor layeris that titanium tungsten (TiW) contributes to the overall resistanceassociated with the thin film resistor layer. In other words, theresistivity of the thin film resistor is not well controlled by thetitanium tungsten (TiW) electrical interface layer, and contributes toincreased thermal stress and an increased thermal coefficient ofresistance (TCR) of the thin film resistor. Another disadvantageassociate with using titanium tungsten (TiW) as an electrical interfacelayer is high particulate levels, as well as maintenance issuesassociated with the high particulate levels.

SUMMARY OF THE INVENTION

The present invention relates to a thin film resistor (TFR) structureand a method of fabricating a TFR structure. The TFR structure includesan electrical interface layer or head layer that is a combination of aTitanium (Ti) layer and a Titanium Nitride (TiN) layer. The combinationof the Ti layer and the TiN layer provides a relatively low resistanceassociated with the electrical interface layer the TFR structure.

In one aspect of the invention, a TFR structure is provided thatincludes a TFR. A first electrical interface portion is coupled to afirst end of the TFR, and a second electrical interface portion iscoupled to a second end of the TFR. The first electrical interfaceportion and the second electrical interface portion are formed of alayer of titanium (Ti) and a layer of titanium nitride (TiN).

Another aspect of the present invention relates to a method offabricating a TFR structure. The method of forming the TFR structureincludes forming a TFR material layer and forming an oxide layer overthe TFR material layer. The TFR needs to be produced using a photoresistand etch process. A first TFR via is formed in the oxide layer over afirst end of the TFR, and a second TFR via is formed in the oxide layerover a second end of the TFR. The TFR vias are etched in the oxide layerusing either wet or dry chemistries or a combination of both. Thephotoresist layer is stripped off after the via etch step. A wetfluorinated etch step using a dilute hydrofluoric acid solution isemployed to clean the surface of the TFR material layer and remove anyremaining oxide. A sputter etch process is then applied to remove nativeoxides which may have built up on the TFR material layer. A layer oftitanium (Ti) is formed over the first and second TFR vias, and a layertitanium nitride (TiN) is formed on the (Ti) layer. The titanium (Ti)layer and titanium nitride (TiN) layer can be etched to form an openingthat defines a first electrical interface portion coupled to the firstend of the TFR layer and a second electrical interface portion coupledto the second end of the TFR layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings.

FIG. 1 illustrates a schematic cross-sectional view of a resultant TFRstructure in accordance with the method of the present invention.

FIG. 2 illustrates a sectional view along line A-A of the resultantstructure illustrated in FIG. 1.

FIG. 3 illustrates a schematic cross-sectional view of a dielectriclayer formed over a metal interconnect layer in accordance with anaspect of the present invention.

FIG. 4 illustrates a schematic cross-sectional view of the structure ofFIG. 3 after deposition of a TFR material layer in accordance with anaspect of the present invention.

FIG. 5 illustrates a schematic cross-sectional view of the structure ofFIG. 4 undergoing an etch step in accordance with an aspect of thepresent invention.

FIG. 6 illustrates a schematic cross-sectional view of the structure ofFIG. 5 after deposition of a dielectric layer in accordance with anaspect of the present invention.

FIG. 7 illustrates a schematic cross-sectional view of the structure ofFIG. 6 undergoing an etch step in accordance with an aspect of thepresent invention.

FIG. 8 illustrates a schematic cross-sectional view of the structure ofFIG. 7 after the etch step is substantially complete in accordance withan aspect of the present invention.

FIG. 9 illustrates a schematic cross-sectional view of the structure ofFIG. 8 undergoing an additional etch step in accordance with an aspectof the present invention.

FIG. 10 illustrates a schematic cross-sectional view of the structure ofFIG. 9 undergoing an additional etch step in accordance with an aspectof the present invention.

FIG. 11 illustrates a schematic cross-sectional view of the structure ofFIG. 10 after deposition of an interface layer in accordance with anaspect of the present invention.

FIG. 12 illustrates a schematic cross-sectional view of the structure ofFIG. 11 undergoing an etch step in accordance with an aspect of thepresent invention.

FIG. 13 illustrates a schematic cross-sectional view of the structure ofFIG. 12 after the etch step is substantially complete in accordance withan aspect of the present invention.

FIG. 14 illustrates a schematic cross-sectional view of the structure ofFIG. 13 after deposition of a dielectric layer in accordance with anaspect of the present invention.

FIG. 15 illustrates a schematic cross-sectional view of the structure ofFIG. 14 undergoing an etch step in accordance with an aspect of thepresent invention.

FIG. 16 illustrates a schematic cross-sectional view of the structure ofFIG. 15 after the etch step is substantially complete in accordance withan aspect of the present invention.

FIG. 17 illustrates a schematic cross-sectional view of the structure ofFIG. 16 after deposition of a contact material layer in accordance withan aspect of the present invention.

FIG. 18 illustrates a schematic cross-sectional view of the structure ofFIG. 17 after undergoing a chemical mechanical polish in accordance withan aspect of the present invention.

FIG. 19 illustrates a schematic cross-sectional view of the structure ofFIG. 18 after deposition of a metal interconnect layer in accordancewith an aspect of the present invention.

FIG. 20 illustrates a schematic cross-sectional view of the structure ofFIG. 19 undergoing an etch step in accordance with an aspect of thepresent invention.

FIG. 21 illustrates a schematic cross-sectional view of the structure ofthe resultant structure after the etch step is substantially complete inaccordance with an aspect of the present invention.

DETAILED DESCRIPTION

The present invention is directed to a thin film resistor structure anda method of fabricating a thin film resistor structure. The thin filmresistor structure includes an electrical interface layer or head layerthat is a combination of a Titanium (Ti) layer and a Titanium Nitride(TiN) layer. The combination of the Ti layer and the TiN layer mitigatesresistance associated with the electrical interface. Additionally, theemployment of the Ti layer provides a more reproducible resistivityvalue associated with the electrical interface layer. Furthermore, theTi layer acts a glue layer to facilitate adhesion of the TiN to the thinfilm resistor material.

FIG. 1 illustrates a cross-sectional view of a thin film resistor (TFR)structure in accordance with an aspect of the present invention. FIG. 2illustrates a sectional view along line 2-2 of the resultant structureillustrated in FIG. 1. A metal interconnect layer 12 resides over adielectric layer 10. The dielectric layer 10 can be formed over asemiconductor structure such as a semiconductor substrate and/or anynumber of intervening layers above a semiconductor substrate. The layersbeneath the dielectric 10 can comprise any number of metal interconnectlevels. An inter-level dielectric layer 14 resides over the metalinterconnect layer 12. The inter-level dielectric layer 14 can comprisesilicon oxide formed using any suitable method including chemical vapordeposition. A thin film resistor (TFR) 16 resides above the inter-leveldielectric layer 14.

The TFR structure has first contact 34 coupled to a first electricalinterface portion 25, and a second contact 36 coupled to a secondelectrical interface portion 27. The first contact 34 has a firstcontact portion 28 and a first conductive portion 30. The second contact36 has a second contact portion 29 and a second conductive portion 32.The first and second contact portions 28 and 29 can be formed from atleast one of tungsten, aluminum, aluminum alloy, copper, copper alloy,or a tungsten alloy. The first and second conductive portions 30 and 32can be formed from at least one of aluminum, aluminum alloy, copper,copper alloy, tungsten, a tungsten alloy or a composite of predominantlyaluminum with small amounts of titanium and titanium nitride.

The first electrical interface portion 25 and the second electricalinterface portion 27 couple the first contact 34 and the second contact36 to respective first and second ends of the TFR material layer 16. Adielectric layer 24 provides electrical isolation between the firstelectrical interface portion 25 and the second electrical interfaceportion 27. Additionally, the dielectric layer 24 overlays the first andsecond interface layers between the first and second contact portions 28and 29. A dielectric layer 26 overlays the dielectric layer 24 betweenthe first and second conductive portions 30 and 32.

The first and second electrical interface portions 25 and 27 are formedof a titanium (Ti) interface layer 20 over the TFR layer 16 and atitanium nitride (TiN) interface layer 22 deposited over the (Ti) layer.The first and second electrical interface portions 25 and 27 are alsoknown as the TF (thin film) Heads, the diffusion layer, the barrierlayer, or the capping layer. The function of the first and secondelectrical interface portions 25 and 27 are to provide electricalconnection to the thin film resistor layer 16, and to protect the thinfilm resistor layer from subsequent pattern and etching processes. Usingthe combination of the Ti layer 20 and the TiN layer 22 on top of the Tilayer 20 as components of the first and second electrical interfaceportions 25 and 27 mitigates resistance associated with the TF head.

The Ti layer 20 functions to provide a more reproducible value of theresistance associated with interface layers 20 and 22 relative to a TiNonly interface layer. Another function of the Ti layer 20 is to lowerthe resistance of the interface layers 20 and 22. The Ti:TiN interfacelayers are compatible with sub-micron metallization process, and providegood thermal stability of the interface to the TFR which results in alower thermal coefficient of resistance (TCR), reproducible resistancevalues, and low particulate levels.

FIGS. 3-18 illustrate a methodology for fabrication of a TFR structureshown in FIGS. 1-2 in accordance with an aspect of the presentinvention. FIG. 3 illustrates an inter-level dielectric layer 54 formedover a metal interconnect 52 (e.g., aluminum, aluminum alloy, copper,copper alloy, tungsten, tungsten alloy) residing over a substrate 50.The substrate 50 can comprise semiconductor devices or circuits.Alternatively, the inter-level dielectric layer 54 can be formeddirectly over a semiconductor substrate and any number of interveninglayers.

The inter-level dielectric layer 54 can comprise silicon oxide formedusing any suitable method including chemical vapor deposition LowPressure Chemical Vapor Deposition (LPCVD), Plasma Enhanced ChemicalVapor Deposition (PECVD), sputtering or high density plasma chemicalvapor deposition (HDPCVD). In one aspect of the present invention, theinter-level dielectric layer 54 is formed using at least one of TEOSsilicon oxides, PECVD silicon oxides, silicon nitrides, siliconoxynitrides, silicon carbides, spin-on glass (SOG) such assilsesquioxanes and siloxane, xerogels or any other suitable material.

In another aspect of the present invention, the thickness of theinter-level dielectric layer 54 is in the range from about 3000 Å toabout 8000 Å, and the thickness of the metal interconnect 52 is in therange from about 3000 Å to about 5000 Å. The inter-level dielectriclayer 54 can be planarized by a chemical mechanical polish (CMP).

FIG. 4 illustrates the structure after a resistor material layer 56 isdeposited over the inter-level dielectric layer 54. The resistormaterial layer 56 can be made from any suitable thin film resistormaterial including nickel chromium (NiCr), a nickel chromium (NiCr)alloy, silicon chromium (SiCr), a silicon chromium (SiCr) alloy,tantalum nitride (TaN), titanium nitride (TiN), or tungsten (W). Theresistor material can be selected based on a desired resistance andstability including the temperature co-efficient of resistance (TCR)associated with the resistor material.

Any suitable technique for forming the resistor material layer 56 can beemployed such as Low Pressure Chemical Vapor Deposition (LPCVD), PlasmaEnhanced Chemical Vapor Deposition (PECVD), sputtering or high densityplasma chemical vapor deposition (HDPCVD) techniques to a thicknesssuitable for forming a TFR. It is to be appreciated, however, that thepresent invention is applicable to other types of thin film formation,such as other deposition techniques (e.g., Physical Vapor Deposition(PVD), Metal Organic Chemical Vapor Deposition (MOCVD), Pulsed LaserDeposition (PLD)) and film growth techniques).

In one aspect of the present invention, the thickness of the TFRmaterial layer 56 is in the range from about 30 Å to about 400 Å, and inanother aspect of the present invention the thickness is in the rangefrom about 100 Å to about 150 Å.

A patterned photoresist layer 59 is deposited over the TFR materiallayer 56. FIG. 5 illustrates the structure undergoing an etch 100 of thelayer 56. The patterned photoresist layer 59 is used to define openingsin the TFR material layer 56 during the etch 100. The photoresist layer59 can have a thickness of about 10,000 Å to about 20,000 Å. However, itis to be appreciated that the thickness thereof may be of any dimensionsuitable for carrying out the present invention.

In one aspect of the invention, the etching process 100 uses either wetor dry chemistries or a combination of both. The photoresist layer 59 isstripped off of the TFR material 56 after the etch step is substantiallycomplete.

FIG. 6 illustrates the deposition of a dielectric layer 58 from whichtwo TFR vias are formed. In FIG. 7, a patterned photoresist layer 60 isapplied out of the surface of the dielectric layer 58. An etch step 200is applied to form the two TFR vias in the dielectric layer 58. The TFRvias are etched using either wet or dry chemistries or a combination ofboth. The photoresist layer 60 is stripped to reveal the generated TFRvias 62, 63 (FIG. 8). After the photoresist layer 60 is stripped, anadditional dilute hydrofluoric acid (HF) wet etch 300 is performed (FIG.9) to remove a small layer of oxide, approximately 100 Å, thick abovethe TFR material layer 56.

FIG. 10 illustrates a sputter etch process 400 applied in a vacuumenvironment to the entire surface of the structure without the presenceof a photoresist layer. The sputter etch process 400 advantageouslyremoves native oxides that build up on the TFR material layer 56, whenit is exposed to atmosphere during previous processing. The first TFRvias 62, 63 form contact pads on the TFR material layer 56.

After the sputter etch process 400 is complete, a titanium (Ti) layer 64is deposited (FIG. 11) into the first TFR vias 62, 63 over the TFRmaterial layer 56 as well as over the remaining portions of thedielectric layer 58. A layer of titanium nitride (TiN) 66 is depositedover the Ti layer 66. The Ti layer 64 and the TiN layer 66 togethercomprise the interface layer (e.g., TF Head or barrier/diffusion layer).Both the Ti layer 64 and the TiN layer 66 can be deposited usingphysical vapor deposition (PVD). The thickness of the Ti layer 64 can bein a range of about 100 to about 300 Å (e.g., 200 Å). The thickness ofthe TiN layer 66 can be in a range of about 800 to about 3000 Å (e.g.,2400 Å).

The effect of the sputter etch process 400 is to lower the interfacelayer resistance and to provide a more reproducible value of theinterface layer resistance. Thus, resistance of the interface layer islowered by applying the sputter etch process 400 to remove the nativeoxides on the TFR material layer 56 before applying the Ti layer 64component of the interface layer, and as well by using specificallyTi:TiN as the interface layer.

FIG. 12 illustrates the structure undergoing an etch 500 of the Ti:TiNlayers 64 and 66. A patterned photoresist layer 68 is employed to forman opening 69 (FIG. 13) during the etch 500 that extends through theTi:TiN layers 64 and 66 to expose a portion of the oxide layer 58, andto separate and electrically isolate the Ti:TiN layers 64 and 66 into afirst electrical interface portion 65 and a second electrical interfaceportion 67. The resultant structure is illustrated in FIG. 13 after theremaining patterned photoresist 68 is stripped. The interface layers 64and 66 can be etched with Chlorine or Fluorine chemistry using magneticenhanced reactive ion etching (MERIE), electron cyclotron etching (ECR),or conventional reactive ion etching (RIE) methods. The chemistry shouldbe highly selective to the Ti:TiN layers 64 and 66 over the underlyingoxide layer 58 and the overlying patterned photoresist 68.

An interlevel dielectric layer 70 is deposited (FIG. 14) over theremaining Ti:TiN interface layers 64 and 66 as well as in the opening 69over the oxide layer 58. A patterned photoresist layer 72 (FIG. 15) isformed on the inter level dielectric layer 70. The patterned photoresistlayer 72 is employed to define second TFR vias 74 and 75 (FIG. 12)during an etch 600 that extends through the inter level dielectric layer70 to expose a portion of the interface layers 64 and 66. The second TFRvias 74 and 75 provide contact openings to the first electricalinterface portion 65 and the second electrical interface portion 67. Theetch 600 is any suitable wet or dry etching process. The resultantstructure is illustrated in FIG. 16 after the remaining patternedphotoresist 72 is stripped.

FIG. 17 illustrates a contact material layer 76 deposition over theremaining dielectric layer 70, and in the second TFR vias 74, 75 overthe exposed first and second electrical interface portions 65 and 67.The contact material layer 76 is deposited employing conventional metaldeposition techniques. The contact material layer 76 can be formed fromone of tungsten, aluminum, aluminum alloy, copper, copper alloy, or atungsten alloy. The contact material layer 76 is planarized by achemical mechanical polish (CMP) to remove the contact material over thedielectric layer 70, and to leave the contact material deposited in thesecond TFR vias 74, 75 to form a first contact portion 78 and a secondcontact portion 79 connected to the first and second electricalinterface portions. The resultant structure is illustrated in FIG. 18.

FIG. 19 illustrates deposition of a metal interconnect 84 over theremaining dielectric layer 70 and in the second TFR vias 78, 79 themetal interconnect layer 84 is deposited employing conventional metaldeposition techniques. The metal interconnect layer 84 can be aluminum,aluminum alloy, copper, copper alloy, tungsten or a tungsten alloy or acomposite of predominantly aluminum with small amounts of titanium andtitanium nitride.

FIG. 20 illustrates the photoresist layer 90 patterned over the metalinterconnect layer 84 to form the interconnect. A timed etch 700 can beemployed with chemistry to etch away the conductive material ormetallization layer 84, until reaching the underlying dielectric layer70. The timed etch 700 of the conductive material layer 84 is performedto form conductive portions 83 and 85 that provide electricalinterconnections to the TFR, such the conductive portions 83 and 85 ofthe conductive material 84 form a continuation of the contact portions78 and 79.

The resultant structure is illustrated in FIG. 21 after the timed etch700 is performed. Following the timed etch 700, the TFR is exposed to anoven baking process (e.g., at 400° C.) to cause the TFR to stabilizeinto defined layers. Any number of intervening layers can then be formedover the resultant structure illustrated in FIG. 21.

What has been described above includes examples and implementations ofthe present invention. Because it is not possible to describe everyconceivable combination of components, circuitry or methodologies forpurposes of describing the present invention, one of ordinary skill inthe art will recognize that many further combinations and permutationsof the present invention are possible. Accordingly, the presentinvention is intended to embrace all such alterations, modifications andvariations that fall within the spirit and scope of the appended claims.

1. A thin film resistor (TFR) structure comprising: a TFR; a firstelectrical interface portion directly coupled to a first end of the TFR;the first electrical interface portion comprising: a first layer oftitanium (Ti) adjacent to the first end of the TFR, and a first layer oftitanium nitride (TiN) formed on the first layer of Ti, wherein thefirst layers of Ti and TiN are located within a first opening formed ina first dielectric overlying the TFR; and a second electrical interfaceportion directly coupled to a second end of the TFR, the secondelectrical interface potion comprising: a second layer of Ti adjacent tothe second end of the TFR, and a second layer of TiN formed on thesecond layer of Ti, wherein the second layers of Ti and TiN are locatedwithin a second opening formed in the first dielectric overlying theTFR; a second dielectric layer located on the first and second layers ofTiN; a first contact extending through the second dielectric layer andcontacting the first layer of TiN; and a second contact extendingthrough the second dielectric layer and contacting the second layer ofTiN.
 2. The TFR structure of claim 1, the TFR formed from one of siliconchromium (SiCr) alloy, nickel chromium (NiCr) alloy, tantalum nitride,titanium nitride, and tungsten.
 3. The TFR structure of claim 1, the Tilayer having a thickness in the range from about 100 Å to about 300 Å.4. The TER structure of claim 1, the TiN layer having a thickness in therange from about 800 Å to about 3000 Å.
 5. The TFR structure of claim 1,the thin film resistor having a thickness in the range of about 50 Å toabout 400 Å.
 6. The TFR structure of claim 1, each of the first contactand the second contact comprising a conductive portion and a contactportion extending from the respective electrical interface portion tothe respective conductive portion.
 7. The TFR structure of claim 6, thecontact portions being formed from at least one of tungsten, aluminum,aluminum alloy, copper, copper alloy and a tungsten alloy, and theconductive portions being formed from at least one of aluminum, aluminumalloy, copper, copper alloy, tungsten, a tungsten alloy and a compositeof aluminum with titanium and titanium nitride.
 8. The TFR structure ofclaim 1, further comprising an oxide layer below portions of the firstelectrical interface portion and the second electrical interface portionwith defined openings that provide electrical contact to the first andsecond ends of the TFR.